The goal of this project is to describe a novel role for the RNA-binding protein Sam68 in synaptic transmission and plasticity. Sam68 is a member of the KH-domain containing family of proteins, which have been linked to the pathogenesis of several neurological disorders via their effects on synaptic transmission. For example, mutations in the KH-family member FMRP result in Fragile X Mental Retardation Syndrome, while mutations in the KH-family member QUAKING have been implicated in Schizophrenia. Two recent studies suggest that Sam68 is involved in the pathogenesis of Fragile X Tremor/Ataxia Syndrome, and Spinal Muscular Atrophy. Elucidation of Sam68's role in maintaining efficient synaptic transmission will provide valuable insights into how dysfunction of the family of KH-domain containing proteins, and Sam68 in particular, leads to neurological disease. Sam68 may serve dual roles at the synapse, first as a modulator of synaptic transmission through NMDA receptor trafficking, and second as a regulator of local protein synthesis at dendritic spines. This proposal includes training in a number of advanced laboratory skills in the fields of electrophysiology and molecular biology in order to conduct a detailed investigation of Sam68's role at the synapse. To study the effects of loss of Sam68 we will use in vivo molecular manipulations (e.g. viral injections), in addition to a complimentary set of experiments using a line of Sam68 null mice. We will examine the effect of loss of Sam68 on NMDA receptor trafficking using whole cell patch clamp recording and quantitative immunohistochemistry. We will examine the ability of Sam68 to regulate local protein synthesis at dendritic spines using fluorescence in situ hybridization, and the photoconvertable fluorescent protein Dendra2. Sam68 may represent a novel regulator of synaptic plasticity by participating in activity-dependent changes involving both receptor trafficking, and local protein synthesis.